1. Field of the Invention
The present invention relates to an inspection apparatus and an inspection method. For example, the present invention relates to an inspection apparatus and method which inspects a pattern formed on an object to be inspected.
2. Related Art
In recent years, with advance in high integration density and large capacity of a large-scale integrated circuit (LSI), a circuit line width required for a semiconductor element increasingly becomes narrow. These semiconductor elements are manufactured such that a pattern is exposed and transferred onto a wafer by using an original pattern (which is called a mask or a reticle and will be referred to as a mask hereinafter) on which a circuit pattern is formed, by means of a reduced projection exposure apparatus which is a so-called stepper to form a circuit. Therefore, in manufacturing of the mask to transfer such a micro-circuit pattern on a wafer, a pattern writing apparatus using an electron beam which can write a micro-circuit pattern is used. A pattern circuit may be directly written on a wafer by the pattern writing apparatus. Alternatively, a laser beam writing apparatus which writes a pattern by using a laser beam in place of an electron beam is attempted to be developed.
For manufacturing an LSI which is manufactured at a high cost, an increase in yield is necessary. However, as typified by a 1-Gbit-class DRAM (random access memory), the size of a pattern configuring an LSI changes from a sub-micron order to a nanometer order. As one of large factors which degrade an yield, a pattern defect of a mask used when ultra-micropattern is exposed and transferred on a semiconductor wafer by a photolithography technique is given. In recent years, with miniaturization of a size of an LSI pattern formed on a semiconductor wafer, a size to be detected as a pattern defect is also very small. For this reason, a pattern inspection apparatus which inspects a defect of a transfer mask used in manufacturing of an LSI requires to be increased in accuracy.
On the other hand, with advance in multimedia, in an LCD (Liquid Crystal Display), an increase in liquid crystal substrate size to 500 mm×600 mm or more and miniaturization of a pattern of a TFT (Thin Film Transistor) or the like formed on a liquid crystal substrate are advanced. Therefore, a very small pattern defect is required to be inspected in a wide area. For this reason, a pattern inspection apparatus which efficiently inspects a defect of a photomask used when patterns of a large-area LCD and a large-area LCD are manufactured within a short period of time must be urgently developed.
As an inspection method, a method of performing inspection by comparing an optical image obtained by picking an image of a pattern formed on a target object such as a lithography mask by using an magnifying optical system at a predetermined magnification, design data, or an optical image obtained by picking an image of the same pattern on the target object with each other is known. For example, as pattern inspection methods, “die to die inspection” which compares optical imaged at a obtained by picking images of the same patterns at different places on the same mask and “die to database inspection” which inputs write data (design pattern data) converted into an apparatus input format to be input by a writing apparatus into a inspection apparatus when a pattern is written by using pattern-designed CAD data as a mask, generates design image data (reference image) on the basis of the write data, and compares the design image data with an optical image serving as measurement data obtained by picking an image of the pattern are known. In the inspection method in the inspection apparatus, a target object is placed on a stage, and a beam scans the target object by movement of the stage to perform inspection. The target object is irradiated with a beam by a light source or an illumination optical system. The light passing through or reflected by the target object is focused on a sensor through an optical system. The images taken on the sensor are transmitted to a comparing circuit as measurement data. In the comparing circuit, after the images are aligned to each other, measurement data and reference data are compared with each other according to an appropriate algorithm. When the measurement data and the reference data are not matched with each other, the presence of a pattern defect is determined (for example, see Published Unexamined Japanese Patent Application No. 2007-102153 (JP-A-2007-102153)).
In a conventional pattern inspection apparatus, an optical image is acquired by using a continuous ultraviolet laser beam. As a light source which generates the ultraviolet laser beam, one large-scale light source such as an ion-laser light source or an excimer laser light source is arranged. Since a fundamental wave generated from the light source is coherent light, in the conventional pattern inspection apparatus, the coherent light is made incoherent through various optical devices. Although the light source itself is a large-scale device, furthermore, for example, various devices to make coherent light incoherent, such as a rotational phase plate and a tetrameric mirror must be arranged. For this reason, in the conventional pattern inspection apparatus, a very large space is disadvantageously necessary to install the pattern inspection apparatus.
As described above, in the conventional pattern inspection apparatus, a large-scale light source such as an ion laser or an excimer laser and various devices to make coherent light incoherent must be mounted. For this reason, the pattern inspection apparatus disadvantageously requires a very large space to install it. In addition, a conventional light source is expensive to increase the cost of the pattern inspection apparatus. Furthermore, various devices to make coherent light incoherent are a factor that increases the cost, as a matter of course.